<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script type="text/javascript" src="../js/vue.js"></script>
</head>
<body>
    <!-- 准备好一个容器 -->
    <div id="root">
       <h2>今天天气很{{info}}</h2>
       <button @click="changeWeather">切换天气</button>
       
    </div>
</body>
<script type="text/javascript">
    Vue.config.productionTip = false //阻止 vue 在启动时生成产生提示
    const vm = new Vue({
        el: '#root',
        data: {
            isHot: true,
        },
        computed: {
            info(){
                return this.isHot ? '炎热' : '凉爽'
            }
        },
        methods: {
            changeWeather() {
                this.isHot = !this.isHot
            }
        },
        watch: {
            //正常写法
            /*isHot: {
                // immediate: false, //初始化时让 handler 调用一下
                // deep: true, //深度监视
                handler(newValue, oldValue){
                    console.log('isHot被修改了', newValue, oldValue);
                }
            },*/

            //简写
            /*isHot(newValue, oldValue){
                console.log('isHot被修改了', newValue, oldValue);
            }*/
        }
    })    

    //正常的写法
    /* vm.$watch('isHot', {
        immediate: false, //初始化时让 handler 调用一下
        deep: true, //深度监视
        handler(newValue, oldValue){
            console.log('isHot被修改了', newValue, oldValue);
     }
    }) */

    vm.$watch('isHot', function(newValue, oldValue){
        console.log('isHot被修改了', newValue, oldValue);
    })
</script>
</html>